Discoloring of the teeth occurs owing to external factors such as adhesion of a colored substance to the teeth surface due to tartar, plaque, smoking, or daily drinking of coffee or tea; and internal factors such as aging which causes discoloration of the dentin appearing through the enamel having high transparency and use of a medicament such as tetracycline during the enamel formation stage, which discolors the enamel itself. In order to fundamentally whiten teeth, it is therefore necessary to take countermeasures against not only the external factors which form colored deposits on the surface but also the internal factors which form internal tooth discolorations.
A variety of physical or chemical methods have heretofore been reported as means for whitening the teeth. Reported as physical methods are, in addition to removal of the colored substance by polishing, a method of removing by using n-butyl ether or butyl butylate (Japanese Patent Laid-Open No. Hei 1-203316, . Japanese Patent Laid-Open No. Hei 1-104004) and a method of improving colored teeth by covering the teeth with ceramic veneers. As the chemical methods, known are a method of promoting remineralization by an oral preparation containing hydroxyapatite (Japanese Patent Laid-Open No. Hei 1-305020, . Japanese Patent Laid-Open No. Hei 9-202718), a method of bleaching with a peroxide (Japanese Patent Laid-Open No. Hei 4-253906), a method of using a dental whitening composition obtained by adding, to a peroxide, a self curing type calcium phosphate compound and a fluoride (Japanese Patent Laid-Open No. Hei 11-116421), a method of promoting remineralization of the enamel by an oral preparation containing a liquefied calcium phosphate compound (Japanese Patent Laid-Open No. Hei 8-319224), or the like.
Application of ceramic veneers needs buffing of the dental surface, whereby the use of the veneers requires guidance and treatment by a dentist. Such dental treatment by experts inevitably costs high amounts. In the method of bleaching with a peroxide, there needs to be a proper concentration of the peroxide for ensuring bleaching of the teeth, whereby such method requires careful treatments according to guidance by an expert.
The method of promoting remineralization by calcium phosphate series compounds such as hydroxyapatite, which has a function to restore the surface of enamel with apatite as its major function for normalization of the teeth, provides unsatisfied results in whitening effects.
Recently, Japanese Patent Laid-Open No. 2002-37721 discloses a method capable of imparting whiteness and gloss to the teeth surface with the use of an oral preparation comprising the following components: (A) 0.02 to 0.7 wt. % (in terms of fluorine atom) of a fluoride ion supplying component; (B) 0.1 to 5 mol/kg of an acid compound having a pKa (25° C.) of 2.5 to 6.0 and the salt thereof; and (C) 5 to 90 wt. % of water, and having a pH, as that of the preparation itself or a 30 wt. % aqueous solution thereof, ranging from 3 to 5.5. Such oral preparation as described in Japanese Patent Laid-Open No. 2002-37721 forms a layer of calcium fluoride on a surface of the teeth to provide whiteness and gloss thereto.